Your key problem, as I understand it, is that this has happened twice....
It is highly likely that you are overdriving your amplifier and then burning up the voice coil or protective resistor(if there is one) on your tweeter.
This happens when you have the music too loud and at which point the bass (requires ooodles or power) draws too much power for your amp to deliver. The amp flatlines or clips...this will burn up everything but usually burns the tweeter first as it requies the least power and can get very hot very fast with a saturated distorted/signal.
It is not the power rating of your amp that is important but whether it is over driven or not. A lower powered amp will run out of power, saturate and clip more easily than a higher powered amplifier. A lower powered amp may actually be more dangerous for your tweeters than a higher powered amp if you like to listen loud. Clean power is good. Sustained distorted power does damage quite quickly.
If the above des not help and you have a very powerful amplifier then it is possible (but unlikely) that the amplifier has a problem affecting BOTH channels.
Note that music from a most top quality consumer systems will not sound loud until it distorts (at which point you risk doing damage).
There are very few consumer systems that can play deafeningly loud without distortion. These systems are usually adapted for or from professional gear.
So as a general advice => if it sounds loud then you probaby have distortion and need to be careful.
As further general advice => music with very heavy bass content is what taxes the amplifier most ...if you enjoy thunderous bass then be more careful or get some pro gear (often with built in soft clipping protection circuitry).
Another suggestion: Tube amps may be less likely to do damage than an SS amp due to the tubes high output impedance and tendency to soft clip. Although tubes generally have lower power ratings to start with.
G'luck and sorry you had these problems but it really not that uncommon especially if you realize that drivers "compress" sound as they heat up (a few minutes of play)....this has a tendency to make people inch up the volume to regain dynamic range and loudness that is lost due to compression => a vicious circle leading to eventual speaker failure.
